The present invention relates to a charge transfer device, such as a CCD and a driving method thereof, and a driving method for a solid-state image sensing device, in particular, it relates to a driving method for CCD solid-state image sensing devices of an IT (Inter-line Transfer) type.
In general, in a CCD solid-state image sensing device of the IT type, when signal charges are transferred, for example, by a vertical charge transfer portion (vertical shift register) having transfer electrodes of four systems, the transfer of signal charges for one line is performed in a horizontal blanking interval, and normally it is performed in a vertical transfer period being composed of eight sectional periods. In respective sectional periods, each one of four transfer electrodes is selectively applied with a high level driving pulse to control a depth of a potential well which is formed under each one of transfer the electrodes of respective systems, and the transfer of signal charges in a vertical direction is realized with the moves of signal charges described in the above. In a case where a read-out method in the interlaced scanning is changed to the read-out method in which all pixels are independently read out, or in a case where a constitution of a CCD solid-state sensing device responds to an electronic zoom lens or correction of blur caused by an unintentional hand move, it is needed to perform the charge transfer in the vertical charge transfer portion at a higher speed than usual.
However, when the transfer speed in the vertical charge transfer portion is made faster, with an increase in the transfer speed, the period of time for accumulating the charges in the vertical charge transfer portion is made shorter. Then the quantity of charges handled in the vertical charge transfer portion is decreased, and there is a fear that the transfer efficiency is lowered. In particular, for a CCD area sensor, there is a tendency that an increase in the number of pixels is demanded to realize high quality images in both a moving picture and a still picture. It is therefore necessary to take measures to such demands as the independent read-out of all pixels, or the improvement in techniques for an electronic zoom lens or correction of blur caused by an unintentional hand move, following to the upward tendency of requiring the increase in the number of pixels. Therefore, it looks inevitable that the transfer speed in the vertical charge transfer portion will continue to go up, so that it is desired to find an effective measure to suppress the decrease in the handling charge quantity in the vertical charge transfer portion.